Molding pulp articles



July 14, 1959 J. E FooTE MOLDING PULP ARTICLES 2 Sheets-Sheet Filed Aug.6. 1956 INVENTOR ATTORNEY July 14, 1959 J. E. FOOTE 2,894,869

, I MOLDING PULP ARTICLES File dAu'g. '6, 1956 2 Sheets-Sheet 2 FIG 4 J.E.FOOTE INVENTOR Bf. Bani. UJ FLMKs ATTORNEY r 2,894,869 rateniedntym;1959 MODDING PULP ARTICLES :James E. Foote, Westport, Conn., assignor toDiamond Gardner Corporation, a corporation of Delaware ApplicationAugust 6, 1956, Serial No. 602,372

4 Claims. (Cl. 162-224) This invention relates to the molding of pulparticles. IMore particularly, the invention relates to methods of:molding in which a series of foraminous molds are advanced successivelythrough an aqueous pulp slurry in -which the articles are formedinitially by the deposition 'of layers of wet pulp on the molds, and thearticles are subsequently compressed and dried to produce az-smooth-surfaced finish thereon.

In the commercial manufacture of molded pulp arti- L cles, such as !pieplates, it is customary to impart a smooth- :surfaced finish to thearticles by employing either one of two well known methods. In one ofthese methods, :the wet initially formed articles are transferreddirectly ffrom the foraminous forming molds to a pair of heatedcompression drying dies, in which all of the excess Water Eris expressedfrom the articles while simultaneously imparting a smooth finishthereto. In the other one of athese methods, the wet initially formedarticles are transfferred from the foraminous forming molds to a drierin which substantially all of the moisture is first removed :1from thearticles by heated air without compressing the :articles, and then thedried articles are subjected to -compression between heated finishingdies. The second ;-method does not produce the desired surfacesmoothness fin the finished articles, and the first method is notsulfitciently economical and rapid for the mass production of low unitcost items, such as pie or household plates, in rtodays highlycompetitive markets.

An object of this invention is to provide a new and improved method formolding pulp articles.

Another object of the invention is to provide a new rand improved methodfor rapidly producing a superior smooth-surfaced finish on molded pulparticles.

Still another object of the invention is to provide a highly economicaland very rap-id method for mold- ;ing pulp articles having a superiorsmooth-surfaced finish.

A method illustrating certain features of the invention :may include thestep-s of initially forming a molded pulp article by depositing a layerof wet pulp onto a :foraminous mold, free or form drying the initiallyformed .article to reduce its moisture content to about 45 to 55% L-byweight, and then subjecting the article to compres- :sion between heateddies to complete the drying operation .and impart a smooth surfacefinish thereto.

Other objects and the nature and advantages of the iinstant inventionwill be apparent from the following description taken in conjunctionwith the accompanying -.-drawings, wherein:

Fig. l is a side elevation of a pulp molding machine :suitable forinitially forming articles in accordance with nnethods embodying theinvention;

Fig. 2 is an enlarged vertical section of a transfer .mechanism and anadjacent conveyor belt located at the discharge station of the moldingmachine illustrated in Fig. 1;

Fig. 3 is a rear elevational view of the transfer mechanism shown inlfig. 2; and v 2 Fig. 4 is a schematic side elevation of one suitablearrangement of apparatus, including a pulp molding machine, a dryingtunnel, and a final compression, and dry.-. ing machine, designed toperform all of the steps of methods embodying the invention. Theinvention may be utilized either in connection with intermittent(step-by-step) or continuously moving machines.

The pulp molding machine illustrated in Fig. 1 is of the intermittentlyoperable type. It includes a series of foraminous forming molds 10located on the periphery of a circular carrier 12 which is disposedvertically and mounted rotatably on a fixed horizontal shaft 14journalled on the main frame 15 of the machine. Each of the molds 10 issecured to the outer end of a hollow arm 16 projecting radially from thecarrier 12, and all of the arms 16 are connected to a central vacuumpump (not shown) which applies suction to the molds 10 during rotationof the carrier 12. The molds are advanced in a circular path in whichthey successively be come immersed in an aqueous pulp slurry containedin a tank 18. The suction applied to the molds 10 while they areimmersed in the tank 18 causes layers of wet pulp to be depositedthereon, thereby initially forming the pulp articles. In the case of themachine illustrated, the articles being produced are pie plates, but

' other molded pulp articles could be formed thereon.

The molds 10 are advanced in a counterclockwise direction, as viewed inFig. 1, from the tank 18 of .pulpslurry through an arc of about 270 to adischarge station where a take-off or transfer mechanism 20 is located.The advancement of the molds 10 is in a uniform step-by-step movement,each step bringing another one of the molds to the transfer mechanism20. A Geneva stop motion is employed for this purpose. A driven member22 secured to the carrier 12 is engaged by a driving member 24 aflixedto a shaft 26 which is operatively connected by gears 28 with a gear 30secured to a main driving shaft 32. The driven member 22 is temporarilylocked at the end of each stepwise movement by means of a bolt 34 whichprojects from one end of a periodically movable crank lever 36 fulcrumedon the main frame 15. A face cam 38 connected to the main driving shaft32 oscillates the lever 36 in timed relation to the intermittentmovement of the carrier 12.

The transfer mechanism 29 removes the initially formed pulp articlesfrom the molds 10 and transfers them one at a time to an adjacent splitendless belt conveyor 40. As is best shown in Fig. 3, the transfermechanism 20 includes three cooperating spaced segments 42 shaped toreceive a pie plate. The segments 42 are secured to threecorrespondingly spaced parallel rocker arms 44 which are aflixed to ahollow rock shaft 46 journalled on the main frame 15 of the moldingmachine. The three rocker arms 44 are movable as a unit through an arcof about between limits adjacent to the paths of the molds 10 and theconveyor 40. The spaces between the segments 42 are aligned with theparallel sections of the split belt conveyor 40, and the arms 44together with their supported segments 42 can be swung slightly belowthe level of the belt conveyor 40, as shown in Fig. 2, to deposit amolded pulp pie plate 48 thereon.

In order to enable the transfer mechanism 20 to engage and remove themolded pulp articles from the molds 10, means is provided for applyingsuction to one of the segments 42. The central segment 42 is providedwith a pair of suction orifices 50 communicating through a duct 52 inits supporting rocker arm 44 with the interior of the hollow shaft 46,which is connected to a suction pump (not shown). An automatic .valve(not shown) is associated with the transfer mechanism 20 forinterrupting the suction when the mechanism is tilted to deposit amolded pulp article on the belt conveyor 40.

An oscillatory movement is imparted to the shaft 46 to rock the transfermechanism 20 in timed relation to the intermittent movement of the moldcarrier 12. This may be accomplished by securing to the shaft 46 a gearsegment 54 which engages a rack 56 formed on the lower end of aninclined movable bar 58 supported on a roller 60 mounted on the mainframe 15. The upper end of the bar 58 is bifurcated and engages a facecam 62 operatively associated with the main driving shaft 32 of themachine.

The molded pulp articles, such as the pie plate 48 produced by themolding machine illustrated in Fig. 1, are still quite wet at the timethey are placed on the belt conveyor 40 by the transfer mechanism 20. Atthis stage of the manufacturing process, the molded pulp articles maycontain from about 70% to about 75% by weight of excess moisture. Thewet pulp articles are rather pliable and soft at this time, yet they aresufiiciently compacted to hold together during the transfer operation.The articles are compacted slightly by the suction applied to the moldsIt? during the initial forming action. The suction is applied to themolds while they are immersed in the aqueous pulp slurry contained inthe tank 13. This slurry is a water suspension of pulp fibers having asolids content of about /2 to about 3% by weight. The suction extractsthe pulp fibers from the slurry and deposits the fibers in layers on themolds, thereby initially forming the molded articles. Suction on themolds 10 is continued while they are advanced by the intermittentlyrotatable carrier 12 through an arc of about 270 to the dischargestation where the transfer mechanism 20 is located. Thus, excessmoisture is sucked from the initially molded articles during the entiretime required for their travel through the 270 arc to the dischargestation, reducing their moisture content to about 70% to 75% by weight.

At this stage of the molding process, the wet pulp articles are ready tobe further dried and compressed to produce the finished articlesdesired, and at this point the treatment of the articles in methodsembodying the invention involves important differences over thetreatments employed in the well known methods of the prior art.

In one of these prior art methods, the wet articles are transferreddirectly from the forming molds to a pair of heated compression dryingdies in which all of the excess water is expressed from the articleswhile simultaneously imparting a smooth finish thereto. Due to therelatively large amount of water which must be expressed by the heatedcompression dies in this method, relatively high temperatures andvpressures must be employed. Consequently, the equipment required iscomplicated, massive and expensive. Even more important is the fact thatthe compression drying step is necessarily unduly slow. As the diescompress the wet pulp it becomes progressively more difficult to removethe remaining moisture (due, at least in part, to the insulating effectof the pulp) and as the efficiency of the drying operation decreasesthere is a corresponding increase in the time required to attaindryness. Furthermore, even if a plurality of drying presses wereemployed to speed up the operation due to practical limitations onmanufacturing floor space, only a limited number of drying presses couldbe employed. Hence, in any event this method of drying imposed a severelimitation on manufacturing capacity.

In another well. known prior are method, known as the semi-smoothingprocess, the wet articles are transferred from the forming molds to adrier in which the preponderantly major portion or substantially all ofthe moisture is first removed from the articles by heated air withoutcompressing the aricles, and then the substantially dry articles aresubjected to compression between heated finishing dies. The hot airdrier reduces the moisture content of the pulp from about 70% down toless than 10%, and the finishing dies remove all of the remainingmoisture. It is evident that the drying equipment required for thismethod is less complicated and expensive than the previously describedequipment. However, the finish produced by this method is inferior tothat produced by the other prior art method described. In attempting tocompress pulp containing less than 10% moisture, enormous resistance tocompression is encountered. Hence, the product is compressed to a lesserdegree, resulting in decreased density and inadequate surfacesmoothness. In an effort to improve the surface smoothness, the surfacesof the articles are sometimes sprayed with additional moisture justbefore placing them in the heated finishing dies, but this results inlittle or no improvement.

In accordance with methods embodying the present invention, the wetarticles are transferred from the forming molds to a free drier in whichthe moisture content of the articles is reduced from about 70 to 75% byweight down to about 45 to 55% by weight, and then the articles aresubjected to compression between heated dies to complete the dryingoperation and impart the desired surface smoothness thereto. By firstreducing the moisture content to about 45 to 55%, the work required toextract the remaining moisture is considerably reduced, therebyeffecting a substantial simplification of the equipment required forfinal drying, and greatly increasing the rate of production. Yetsuflicient moisture remains to maintain the pliability and softnessrequired to produce good surface smoothness. In fact, the surfacesmoothness produced by methods embodying the invention is much superiorto that heretofore obtainable.

One type of apparatus suitable for performing all of the steps ofmethods embodying the invention is illustrated schematically in Fig. 4.This apparatus includes a pulp molding machine 70 which may correspondin structure and in operation to the previously described pulp moldingmachine illustrated in Fig. l. The machine 70 comprises a series offoraminous molds 72 mounted on the periphery of an intermittentlyrotatable circular carrier 74. Rotation of the carrier 74 advances themolds 72 through an arcuate path in a counterclockwise direction, asviewed in Fig. 4, from a tank 76 containing liquid pulp slurry to atransfer mechanism 78, which corresponds to the mechanism 20 illustratedin Figs. 1, 2 and 3. Suction applied to the molds 12 while they aresubmerged in the pulp slurry causes the deposition of layers of pulp onthe molds, to initially form the articles. The suction is continuedwhile the molds 72 are advanced successively from the tank 76 to thetransfer mechanism 78, thereby lightly compacting the molded articlesand reducing their moisture content to about 70 to 75 by the time theyreach the transfer mechanism 78 and are transferred to an endless beltconveyor 80.

The wet articles are advanced by the conveyor 80 through an elongatedhorizontal drying tunnel 82 in which the articles are subjected to anysuitable free drying treatment. For example, the articles may besubjected to a current of heated air therein. This treatment reduces themoisture content of the articles from about 70% down to about 45 to 55%by weight. A value of about 50% moisture is preferred, a value between45 and 55 is desired and is considered optimum, and values rangingbetween 35 and 65% may in some instances be considered acceptable.

After emerging from the tunnel 82, the partially dried articles areadvanced by the conveyor 80 to a transfer mechanism 84, which is similarto the transfer mechanism 78. Here the articles are transferred one at atime from the conveyor 80 to a final compression and drying machine 86comprising a series of male compression dies 88 mounted on the peripheryof an intermittently rotatable carrier 90 which advances the articles toa vertically reciprocable female compression die 92. During each dwellin the step-by-step movement of the carrier 90, one of the pulp articlesis subjected to final compression and drying between the male die 88carrying the article and the female die 92. Another transfer mechanism94 then discharges the completed articles from the machine 86 to aconveyor 96 which transports the articles to a suitable stacking andstorage area (not shown).

The type of apparatus illustrated in Fig. 4 is particularly suitable forperforming methods embodying the invention at a relatively high rate ofproduction. However, it is evident that other types of apparatus mayalso be employed for this purpose. It is contemplated that the pulpmolding machine employed may be of the continuously operable typeinstead of the step-by-step type machine illustrated and describedherein. In order to increase the production capacity of the step-by-steptype of machine, it may be considered desirable to employ a pair ofalternately operable transfer mechanisms instead of the single mechanismshown. In such case, it may be possible to double the capacity of theproduction line by employing two drying tunnels and two finalcompression and drying machines.

Regardless of what type of apparatus may be employed, methods embodyingthe present invention provide a highly economical and rapid system forthe mass production of low unit cost items, such as molded pulp pie orhousehold plates. In the production of such items in immense quantities,it is vital to reduce manufacturing costs to the strictest minimum. Evena small fraction of a cent shaved from the cost of producing each itemis worthy of careful consideration. Among the primary advantagesobtainable from methods embodying the invention are a substantialsimplification of the equipment required for final drying and a greatlyincreased rate of production, while at the same time producing asuperior final product.

It will be obvious to those skilled in the art that various changes maybe made Without departing from the spirit of the invention and thereforethe invention is not limited to what is shown in the drawings anddescribed in the specification but only as indicated in the appendedclaims.

What is claimed is:

1. A method of molding pulp articles, comprising the steps of immersinginto a liquid pulp slurry a formainous mold under suction to deposit alayer of wet pulp thereon which initially forms a molded pulp article,removing the mold from the slurry While continuing the suction to reducethe moisture content of the deposited pulp article to about 70% to 75%by weight free drying the wet pulp article to reduce its moisturecontent down to about to by weight without compressing the article, andthen subjecting the partially dried article to compression betweenheated dies to remove the remaining moisture and impart a smooth surfacefinish to the article.

2. The method defined by claim 1, in which the moisture content of thearticles is reduced to about 50% by weight in the free drying step.

3. A method of molding pulp articles, comprising the steps ofcontinuously advancing a series of foraminous molds through a liquidpulp slurry while applying suction to the molds to deposit layers of wetpulp thereon which initially form molded pulp articles, successivelyremoving the molds from the slurry while continuing the suction toreduce the moisture content of the deposited pulp articles down to aboutto by weight, subjecting the articles to a current of heated air toreduce their moisture content down to about 45% to 55% by weight withoutcompressing the articles, then successively transferring the articles toheated compression dies, and compressing the articles between the heateddies to remove the remaining moisture and impart a smooth surface finishthereto.

4. The method defined by claim 3, in which the moisture content of thearticles is reduced to about 50% by weight by the current of heated air.

References Cited in the file of this patent UNITED STATES PATENTS2,369,488 Perry Feb. 13, 1945 2,559,945 Chaplin July 10, 1951 2,704,493Randall Mar. 22, 1955 2,746,358 Emery May 22, 1955

1. A METHOD OF MOLDING PULP ARTICLES, COMPRISING THE STEPS OF IMMERSING INTO A LIQUID PULP SLURRY A FORMANIOUS MOLD UNDER SUCTION TO DEPOSIT A LAYER OF WET PULP THEREON WHICH INITIALLY FORMS A MOLDED PULP ARTICLE, REMOVING THE MOLD FROM THE SLURRY WHILE CONTINUING THE SUCTION TO REDUCE THE MOISTURE CONTENT OF THE DEPOSITED PULP ARTICLE TO ABOUT 70% TO 75% BY WEIGHT FREE DRYING THE WET PULP ARTICLE TO REDUCE ITS MOISTURE CONTENT DOWN TO ABOUT 45% TO 55% BY WEIGHT WITHOUT COMPRESSING THE ARTICLE AND THEN SUBJECTING THE PARTIALLY DRIED ARTICLE TO COMPRESSION BETWEEN HEATED DIES TO REMOVE THE REMAINING MOISTURE AND IMPART A SMOOTH SURFACE FINISH TO THE ARTICLE. 